A typical wireless communication system includes a number of base stations each operating to provide coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices, whether or not user operated. In turn, each base station may sit as a node on a core access network that includes entities such as a network controller, switches and/or gateways, and the core network may provide connectivity with one or more external transport networks such as the public switched telephone network (PSTN) and the Internet. With this arrangement, a UE within coverage of the system may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Such a system may operate in accordance with a particular air interface protocol, examples of which include, without limitation, Long Term Evolution (LTE) (using orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), and BLUETOOTH. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between base station coverage areas, and other functions.
Further, each base station may provide wireless service to UEs on one or more carrier frequencies, with the air interface defining various downlink and uplink channels. For instance, on the downlink, the air interface may define a reference channel for carrying a reference signal that UEs can measure to evaluate base station coverage strength, the air interface may define various other downlink control channels for carrying control signaling to UEs, and the air interface may define one or more downlink traffic channels for carrying bearer data (e.g., application-layer communications) and other information to UEs. And on the uplink, the air interface may define an access channel for carrying UE access requests to the base station, the air interface may define one or more other uplink control channels for carrying control signaling to the base station, and the air interface may define one or more uplink traffic channels for carrying bearer data and other information to the base station.
When a UE initially enters into coverage of such a system, the UE may scan for a strongest base station coverage area in which to operate, and the UE may then engage in signaling with and via the base station, to register for service. The UE may then be served by the base station in a connected state in which the UE has an established radio-link-layer connection with the base station through which the UE and base station may exchange bearer data, facilitating communication by the UE on the external transport network for instance.
When so served, the UE may from time to time also monitor coverage strength from its serving base station and from adjacent base stations, to help ensure that the UE is served with sufficiently strong coverage and perhaps with the strongest available coverage. If the UE's coverage from its serving base station becomes threshold weak and/or if another base station's coverage becomes threshold strong (e.g., threshold stronger than the serving base station's coverage or than a defined level), then the UE may engage in signaling with its serving base station, and the serving base station may take action to coordinate handover of the UE to the other base station.